1. Field of the Invention
The field of invention is telescopes used for various terrestrial and sky viewing interests and needs. This type of device is generally covered under patent class 359 (although other classes are also relevant to aspects of the invention). Reflector telescopes (those using a "primary mirror") are the sub-field of telescopes affected by the invention.
2. Description of Prior Art
For several years preceding the invention I purchased and/or built several telescopes for different purposes. Both land viewing and amateur astronomy were among my interests. I found that a reflector telescope was the most cost-efficient viewing instrument for many applications. I also discovered that when I wanted to use one telescope for various purposes (e.g. land viewing and astronomy) I had to buy expensive accessories, accept compromised viewing options, and/or buy a new telescope more appropriate to my specialized viewing interests. After I had acquired several telescopes and numerous accessories for different purposes and sub-purposes (e.g. viewing nebula vs. planets in astronomy), I intensified my search for strategies to make one reflector telescope more versatile. During the summer of 1996 I got an idea which is the basis of this invention. The idea involved finishing a primary mirror on two sides with different focal ratios and providing mechanisms to flip the mirror and adjust the scope for different viewing options. Initially I did not know whether the idea was new so I conducted an extensive review of literature concerning currently available commercial telescopes. The only "mirror flipping" strategies which I discovered in current use for telescopes involved diverting light at or near the telescope's eyepiece to facilitate astronomical photography and other viewing options. No primary mirror flipping strategy was discovered. When I found no telescope similar to the one which I had conceived, I did an extensive library and computer-based search of patent records. Patent classes 359, 33, 356, 264, 269, 362, 396, 227, 427, 428, 234, and 353 were among the areas searched. Again I found no similar devices. I then began to develop the idea to a concrete set of strategies and mechanisms for production. In July 1997 I prepared an initial description of the invention. That description was reviewed and witnessed by several people. Also beginning in 1997, I began sub-set prototype development and created specifications for optics to support the invention. During the prototype development process initial specifications were refined and expanded and preferred initial deployment strategies were selected. This document describes the invention as currently conceived and developed through limited prototype development.
The basic strategy for a reflector telescope was invented several hundred years ago. In 1672 Isaac Newton was attributed with the development of a workable reflector telescope. The use of glass as the substrate for primary mirrors in reflectors is attributed to Leon Foucault in 1856. Telescopes which implement many of the strategies of Newton and Foucault are called "Newtonians". Other reflector scopes, e.g. Cassegrains, have further developed and refined the basic light reflection, magnification and focus strategies of the Newtonian. Many devices such as eyepieces, finder scopes, mirror cells, alternate aiming devices, mounts, tracking systems, etc. have been developed over the centuries to supplement and improve on the basic reflector telescope design. This invention utilizes basic Newtonian and Cassegrain designs and supplements them with added value. Added value results from the addition of multi-focal-ratio capacity to the primary mirror. Several dual-focal-ratio embodiments of this multi-focal-ratio primary mirror invention are described in this application.
Currently, "reflector" telescopes can provide a cost-efficient way of viewing distant objects under magnification. However, the efficiency and precision of long-distance viewing with these devices varies by telescope design. The "focal ratio" of a reflector telescope is a prime determiner of effective light-gathering, field of view, and magnification of the object observed. Different focal ratios provide viewing advantages and disadvantages depending upon distance between the observer and the object being viewed and viewer preferences for lighting, magnification and field of view.
The "primary mirror" is the principle light-gathering, transfer, and focus-causing agent for a reflector telescope. Currently, reflector telescopes available for both astronomical and terrestrial observation are limited by a single fixed-focal-ratio of the scope's primary mirror. The mirror is cut to a precise surface curve and coated for reflection on one face. The curve at which the mirror is cut determines the scope's focal ratio. And, the focal ratio determines point of focus, effective light gathering, and magnification. The mirrored surface is backed by a hard substrate to provide the rigidity necessary to maintain a precisely cut and finished curve (e.g. a parabola). Variance in magnification is provided by structures remote from the primary mirror such as intervening lenses, secondary mirrors, or most commonly by eyepieces. But all use of the telescope is limited to the functions feasible for the single focal ratio of the selected primary mirror.
As a result a telescope built with a single-focal-ratio primary mirror is either specially made for limited purposes or is a compromise for general use. The functional problems with this are many. For example, in astro-photography or "deep sky" observation, a short focal ratio primary mirror is often preferable because of a wider field of view and the fact that more effective light is passed to the camera and/or eyepiece. However short focal ratio mirrors provide less image magnification helpful for such functions as planetary observation. Therefore telescope users who want to view objects which are better seen with different focal ratios select among numerous eyepieces, choose a scope which provides a compromise fixed-focal-ratio, or they buy more than one scope. The disadvantages of numerous eyepieces include their cost and the fact that they do not change the instrument's focal ratio which is a primary determiner of effective light gathering. The disadvantage of a compromise focal ratio is that often none of the viewing options precisely match the need of the user. Problems with the procurement of multiple scopes include such issues as duplication of many costs for manufacturers and product users, waste of materials, lack of portability, and excessive storage requirements.
As mentioned earlier, the current art for primary mirrors involves creating reflection capability on one face only, and using a substrate thickness proportionate to the mirror diameter. This proportional relationship is determined by the type of material from which the mirror substrate is made. The primary purpose of the substrate is to maintain rigidity of the mirror's reflective curve under normal variance of use in different atmospheric conditions. (For a Pyrex mirror for example, the estimated optimal ratio is about six to one--diameter to thickness. Therefore a six-inch wide mirror would be about one inch thick to maintain the desired surface curve under varying conditions.)